1. Field of the Invention
This invention relates to breathing equipment for aircrew.
2. Description of the Related Art
The normal breathing equipment for aircrew comprises a flexible face mask having an inspiratory valve supplied with oxygen or some other breathable gas and an expiratory valve to allow the pilot to expel the air from the mask on exhalation. The face mask is attached to the pilot's helmet by means of a harness incorporating a releasable fitting.
In fighter aircraft, it is necessary that the face mask makes a proper seal with the pilot's face at all times. Under normal flying conditions, this is not a problem as the pilot adjusts the harness tension so that it makes the necessary seal and is also comfortable to wear. The supply of the breathable mixture through the mask is controlled by a breathing gas regulator which is responsive to the G-forces that it is subject to. In other words, when the G-force increases, the pressure of the gas supply is correspondingly increased and vice versa. Thus, changes in the G-forces applied to the regulator controlling the breathable gas supply result in automatic changes in pressure in the interior of the mask. It will be appreciated that unless some suitable means are provided to improve the seal between the mask and the pilot's face, any increase in pressure within the mask cavity will cause the mask seal to leak to atmosphere so the pilot will not receive the pressure of breathable gas he requires and could black-out. This condition will be critical, particularly in a combat situation.
One known way of overcoming this problem has been to provide an over-centre toggle in the harness assembly attaching the mask to the helmet. The over-centre toggle is in its non-tensioned position for normal flight but, when the pilot wants to make a tight turn, he moves the toggle into its tensioned position before he makes the turn thereby increasing the tension on the face mask and improving its seal on his face. After the turn is completed, the pilot then releases the toggle. Indeed he has to do this because the pressure exerted on his face when the toggle is engaged is so great that it is very uncomfortable. The main problem with this arrangement is that the pilot has to remember to engage the toggle before he makes a turn (possibly difficult in a combat situation). Furthermore, he must release the toggle after the turn as the pressure on his face is too high to be comfortable for normal flying.
In another known solution, the problem of the pilot having to normally tension the toggle on the facemask each time he makes a turn is overcome by connecting the facemask inlet hose, supplied by the regulator to a bladder situated in the pilot's helmet between the back of his head and the inside of the helmet. With this arrangement, when the regulator automatically increases the breathable gas pressure to the facemask, the bladder is inflated and pushes the rear of the helmet away from the rear of the pilot's head.
Because the breathing mask is attached to the helmet by means of the harness arrangement which is inextensible, the breathing mask is drawn towards the pilot's face thereby increasing its sealing capability and coping with the increased pressure of the gas supplied to the interior of the mask. After the turn has been completed, the regulator automatically reduces the gas supply pressure so the bladder is correspondingly deflated and the increased mask pressure on the pilot's face is reduced accordingly. Thus, it will be appreciated that with this system, automatic adjustment of the pressure exerted by the mask on the pilot's face is achieved, this pressure being dependent on the G-forces generated by the aeroplane during flight which are sensed by the regulator controlling the breathable gas supply.
Whilst it might appear that a helmet incorporating a bladder provides an excellent solution to the problem of continually adjusting the pressure of the mask on the pilot's face, there is a serious problem with this arrangement because fighter pilots in the future will have avionic systems attached to their helmets incorporating an armament sight which the pilot has to look through in order to direct his fire power on the target. This sight normally comprises an arm or the like attached to the helmet and extending forwardly therefrom into the pilot's line of vision. Thus, everytime the pilot's helmet moves, the sight will also move. It will be appreciated therefore that such a sighting system cannot be satisfactorily used with a breathing system which necessitates the helmet to move to improve the sealing of the facemask on the pilot's face as the sight will not work accurately. Thus, avionic systems cannot be used effectively with a helmet of this type.
It is therefore an object of the present invention to provide an improved facemask for use with an aircrew flying helmet which overcomes or substantially reduces the problems of the prior art by causing the face-piece to which the breathable gas is supplied rather than the pilot's helmet to be moved towards the pilot's face and thus increase the seal therewith when the pressure of the breathable gas supplied to the interior of the mask increases above that required for normal breathing and vice versa. By keeping the pilot's helmet stationary at all times and dynamically moving the facemask in relation thereto, avionic systems can be attached to the helmet which will work satisfactorily.